The present invention relates to apparatus for feeding, transporting and manipulating sheets (especially groups of sheets in the form of book sections or signatures) in bookbinding machines. More particularly, the invention relates to improvements in apparatus of the type wherein a first conveyor means transports stacks of sheets (hereinafter called stacks of signatures) to a location at which a suitable mechanism transfers successive signatures of a stack onto further conveyor means for introduction into the book assembling unit or units of the machine. Still more particularly, the invention relates to improvements in apparatus wherein fresh stacks of signatures are moved seriatim into abutment with the last signatures of the preceding (expiring) stacks to insure continuous delivery of signatures to the transferring mechanism.
U.S. Pat. No. 3,416,679, granted Dec. 17, 1968 to Gualandris et al., discloses an apparatus wherein two discrete chain or belt conveyors are driven independently of each other. One of the conveyors is in continuous motion and serves to deliver signatures into the range of the transferring mechanism. The other conveyor is started only when the supply of signatures on the one conveyor is nearly exhausted and serves to deliver a fresh stack of signatures. A drawback of such coventional apparatus is that they are quite complex, expensive and prone to malfunction. Moreover, an unskilled or careless operator is likely to start the wrong conveyor at an inopportune time; this invariably entails long-lasting interruptions in operation of the bookbinding machine.